Studies of the trypan blue treated rat as an experimental model of Hodgkin's Disease will continue. Emphasis will be placed on the following: 1) the mechanism underlying sequential involvement of lymph nodes beginning at the hilus of the liver and anterior mediastinum and subsequently nodes at the upper end of the thoracic duct axilla; 2) mechanisms underlying the deposition and retention of hemosiderin in reticular cells of these nodes and in hepatic tumor deposits; 3) correlation between the radiographic and histologic appearance of nodes in experimental animals with that of involved nodes in patients with Hodgkin's Disease.